1. Field of the Invention
This invention relates to the forming of isolation or field oxide in a semiconductor device, (namely, an integrated circuit,) and more particularly, to a method of forming such oxide which eliminates the "bird-beak" extension of the oxide commonly formed as a part of the isolation oxide. This invention also relates to the resulting structure.
2. Prior Art
In U.S. Pat. No. 3,648,125 entitled "Method of Fabricating Integrated Circuits with Oxidized Isolation and The Resulting Structure", on an invention of Douglas L. Peltzer, the importance of electrically isolating a plurality of pockets of semiconductor material through the use of field or isolation oxide is disclosed. The advantages of such oxide isolation are set forth in that patent, and the use thereof has become widespread.
As is well known, it is highly desirable to keep the isolation oxide area as small as possible so that the number of devices which can be placed on a wafer is maximized. Meanwhile of course, the isolation function cannot be compromised.
In a known example of oxide isolation growth, reference is made to U.S. Pat. No. 4,118,728, entitled "Integrated Circuit Structures Utilizing Conductive Buried Regions" invented by Robert Berry. With reference to FIGS. 2 and 3 thereof in particular, oxide and nitride layers are patterned on an epitaxial layer of a semiconductor structure. The oxide layer is generally required to reduce the generation of defects during the isolation formation process. Because of the exposed edges of this oxide layer, when field oxide is subsequently grown, the field oxide takes the shape shown in FIG. 3, defining the bird-beak regions which in fact lift the nitride layer edges. These bird-beak formations reduce to an extent the packing density of devices which can be achieved by encroaching into active regions of the device. That is, if such bird-beak regions could be eliminated, the oxide isolation regions could be moved closer together without sacrificing size of the active device region therebetween. This would result in the ability to position active device regions more closely together, without sacrifice of oxide isolation effectiveness and thus increase device packing density.